Quantitative analysis of surrounding rock damage induced by different blast hole types in drift blasting

To quantify the impact of the blast hole type on drift surrounding rock damage, on-site sequential blasting tests were conducted in slightly weathered gabbro. High-frequency ground-penetrating radar (GPR) was used to measure the sidewall damage after cut, auxiliary, and contour hole blasting to obtain damage contribution data. To acquire the damage data at all typical locations, a 3D LS-DYNA numerical model for sequential blasting-induced damage was established. The reliability of the model was verified using GPR data. Because rock mass damage in numerical simulations is typically characterized by a damage factor (which can take on multiple values), a correlation was established between the measured damage and the values of this factor obtained from the simulations. The cumulative damage characteristics and evolution laws at different locations were revealed. The results showed: 1) GPR-measured damage depth matched the simulated depth at a damage factor of 0.3, which was set as the rock mass damage threshold. 2) The surrounding rock damage depth at the hole bottom plane was 55.7%–63.7% of that at the hole collar plane, with severe damage depths accounting for 58.4% and 70.2% of the two planes, respectively. 3) Within 0.8 m from the hole collar, sidewall damage was caused by the combined action of auxiliary and contour holes, with auxiliary holes’ contribution reaching a maximum of 37.1%; between 0.8 and 1.08 m, the contribution of auxiliary holes decreased, and damage became dominated by contour holes; beyond 1.08 m, damage was primarily attributable to contour holes. Vault damage was primarily induced by contour holes, whereas floor damage was caused by cut and bottom holes, with a maximum cut-hole contribution of 22.1%. These findings provide a reference for surrounding rock damage control and blast hole parameter optimization in slightly weathered gabbro.